Semiconductor integrated circuits operate based on at least one power supply voltage. For example, the semiconductor integrated circuits may directly use an external voltage that is provided from an external circuit as the power supply voltage, or may include a power supply circuit that generates the power supply voltage based on the external voltage. The power supply voltage should be stable for driving the semiconductor integrated circuits. Researchers are conducting various research projects on techniques of designing power supply circuits that output a power supply voltage having a fixed level, regardless of different input voltages having different levels.